Question 19N.3.hl.TZ0.24
| Date | November 2019 | Marks available | [Maximum mark: 6] | Reference code | 19N.3.hl.TZ0.24 |
| Level | hl | Paper | 3 | Time zone | TZ0 |
| Command term | Deduce, Describe, Explain | Question number | 24 | Adapted from | N/A |
Steroids are lipids with a steroidal backbone. The structure of cholesterol is shown in section 34 of the data booklet.
Infrared (IR) spectroscopy is used to identify functional groups in organic compounds.
Deduce the wavenumber, in cm−1, of an absorption peak found in the IR spectrum of testosterone but not in that of cholesterol.
[1]
1700−1750 «cm−1» ✔
NOTE: Accept a specific wavenumber value within range.
Describe a technique for the detection of steroids in blood and urine.
[3]
Any three of:
sample/liquids vaporized «in oven/at high temperature»
OR
sample injected into mobile phase/inert gas
OR
nitrogen/helium/inert gas acts as mobile phase
OR
sample carried by inert gas «through column» ✔
NOTE: Award [1 max] for identifying suitable technique (eg GC-MS etc.).
Do not accept just “gas”.
Accept description of HPLC using liquid mobile phase.
stationary phase consists of a packed column
OR
packing/solid support acts as stationary phase ✔
NOTE: Accept named stationary phase, such as «long-chain» hydrocarbon/polysiloxane/silica.
components separated by partition «between mobile phase and stationary phase»
OR
gases/liquids/components have different retention times/Rf
OR
gases/liquids/components move through tube/column at different speeds/rates ✔
detector/mass spectrometer/MS «at end of column»
OR
databases/library of known fragmentation patterns can be used ✔
NOTE: Accept “area under peak proportional to quantity/amount/concentration of component present «in mixture»”.
Explain how redox chemistry is used to measure the ethanol concentration in a breathalyser.
[2]
ALTERNATIVE 1
oxidizing agent/«acidified» potassium dichromate(VI) converts ethanol to ethanoic acid ✔
colour change «from orange to green» is measured/analysed «using photocell» ✔
ALTERNATIVE 2
ethanol is oxidized to ethanoic acid «at anode and oxygen is reduced to water at cathode» ✔
current/voltage/potential is measured «by computer»
OR
current/voltage/potential is proportional to ethanol concentration ✔
NOTE: Accept names or formulas for reagents.
Accept “«acidified» dichromate/Cr2O72−” for “K2Cr2O7”.
Award [1 max] for "Cr(VI) going to Cr(III) AND colour changing/colour changing from orange to green".
Do not penalize incorrect oxidation state notation here.
Accept "EMF" for "voltage".